It’s a tough call. Having the Save button disabled tells you that you haven’t modified anything (and makes it possible to warn users that they are leaving a page without saving it).
Since It’s All Text is outside of MODx, MODx has no easy way of telling that the field has been modified since no keypress events have occurred inside MODx. I’m not sure how the dirty flag is currently set, so it might be possible to detect it, but that would waste resources for everyone you doesn’t use It’s All Text.
You could certainly file it as a feature request.
Or, better yet, you could develop a first-class code editor plugin for MODx.
BTW, have you tried CodeMirror?